The present invention relates to an electric wire and a coil, and more particularly, the present invention relates to an electric wire and a coil used for a winding wire, a litz wire, a cable, and the like in various types of high frequency devices.
In winding wires and power cables of devices to which high frequency current is applied (such as transformers, motors, reactors, induction heaters, and magnetic head devices), a magnetic field generated by the high frequency current causes an eddy current loss within a conductor. As a result, AC resistance increases (a skin effect and a proximity effect increase). This causes heat generation and increases power consumption. General countermeasures to prevent the increase of the skin effect and the proximity effect include a reduction in diameter of wires and an employment of litz wires in which strands are individually subjected to insulation covering (refer to, for example, Patent Literature 1 (Japanese Patent Application Laid-open Publication No. 2009-129550), Patent Literature 2 (Japanese Patent Application Laid-open Publication No. 62-076216), Patent Literature 3 (Japanese Patent Application Laid-open Publication No. 2005-108654), Patent Literature 4 (International Publication No. 2006/046358) and Patent Literature 5 (Japanese Patent Application Laid-open Publication No. 2002-150633)).
However, in the prior art described in Patent Literatures 1 to 5, there is a limit of the reduction in diameter of the wires because of difficulty of the process of removing insulation films of the wires during a solder treatment for wire connection and because of an increase in the number of strands. In addition, effective measures to prevent the AC resistance have not been found in wires with diameters in which the proximity effect is overwhelmingly dominant compared with the skin effect, and the fact that characteristics obtained by the reduction in diameter are limited is a matter of common knowledge. Although Patent Literatures 1 to 5 describe examples of the measures against the AC resistance, these examples are not effective measures because these are conceptional and lack concreteness.
Patent Literature 6 (Japanese Utility Model Application Laid-open Publication No. 50-066171) describes a structure in which the periphery of an aluminum (Al) conductor is covered with a copper layer, and a nickel layer is formed thereon. However, the structure is not used in order to decrease AC resistance because the nickel layer is merely formed for ease of soldering.
Patent Literature 7 (Japanese Patent Application Laid-open Publication No. 2010-157363) and Non-Patent Literature 1 (Tsutomu Mizuno and seven others; “Reduction in Eddy Current Loss in Conductor Using Magnetoplated Wire”, The Journal of the Institute of Electrical Engineers of Japan A, 2007, Vol. 127, No. 10, p. 611 to 620) and Non-Patent Literature 2 (Tsutomu Mizuno and seven others; “Reduction of Eddy Current Loss in Magnetoplated Wire”, The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, 2009, Vol. 28, No. 1, p. 57 to 66) each teach that the periphery of a copper (Cu) wire is plated with a soft magnetic material layer (a magnetic thin film) in order to decrease AC resistance. However, the soft magnetic material layer (the magnetic thin film) cannot completely prevent an external magnetic field from entering therethrough. As a result, a loss due to the proximity effect increases because the unavoidable external magnetic field causes eddy currents.